Science | Paleontology
Adapted to the cold, they survived a succession of global winters that killed the reptiles that until then dominated terrestrial ecosystems.
Dinosaurs became the dominant land animals because some were adapted to the cold, say the authors of a study published in the journal Science Advances. 202 million years ago, at the end of the Triassic, a mass extinction occurred. The large reptiles that had dominated the terrestrial ecosystems disappeared and gave way to the dinosaurs. How did these survive? Paleontologist Paul Olsen and his collaborators say it was possible because there were groups of dinosaurs adapted to living in cold climates.
The Triassic and Jurassic world was hot and humid. All the emerged lands were on a continent, Pangea, which began to break up at the beginning of the Jurassic when the crack that is now the Atlantic Ocean opened. Atmospheric concentrations of carbon dioxide (CO2) hovered around 2,000 parts per million, up from 421 today. There is no evidence that polar ice caps existed, there were deciduous forests at the poles and temperatures in the tropics reached 60 degrees. However, despite the high concentration of CO2, some climate models suggest that high latitudes were cold during parts of the year receiving little sunlight.
Scientists don't know exactly what happened 202 million years ago. If the great extinction was caused by a planetary impact, like the one that ended the reign of the dinosaurs 66 million years ago, or a series of gigantic volcanic eruptions, the hypothesis that Olsen and his collaborators start from. According to them, the sulfur ejected by the volcanoes deflected so much sunlight that it caused repeated global winters in which the tropics may even have frozen. Three quarters of marine and terrestrial species became extinct, including all large reptiles. Burrowing turtles and some primitive mammals survived, and the reign of the dinosaurs began.
Researchers present the first evidence that Triassic dinosaurs also thrived in cold environments: traces of these animals next to rock fragments that could only have been deposited by ice, from China's Junggar Basin, which was 202 million years ago. at about 71 degrees north. When polar cold snaps spread to the rest of the world as a result of massive eruptions, northern dinosaurs were adapted to survive in that colder world.
“Dinosaurs were there during the Triassic, under the radar the whole time. The key to his final mastery was very simple. They were animals fundamentally adapted to the cold. When it was cold everywhere, they were prepared, and other animals were not," explains Olsen. Although they arose 231 million years ago in temperate latitudes, the dinosaurs reached as far north as Pangea 214 million years ago. The authors believe that feathers could have played a key role in the cold adaptation of dinosaurs.
Paleontologists have accumulated evidence in recent decades that many dinosaurs, including the popular tyrannosaurus, had primitive feathers. Although birds use them to fly, non-avian dinosaurs –those that became extinct and did not become birds– were able to use them for courtship, but Olsen and his colleagues believe that their main purpose was something else, thermal protection.
“Extreme winter events during volcanic eruptions may have brought freezing temperatures to the tropics, which is where many of the extinctions of large, naked, featherless vertebrates appear to have occurred. Whereas our good feathered friends acclimatized to cooler temperatures at higher latitudes did just fine," says geologist Dennis Kent, one of the study's co-authors.